CN116359582A - Current sensing with positional stability - Google Patents

Abstract

A sensing system for contactlessly sensing a current is provided. The system comprises: a conductor for generating a magnetic field when a current flows through the conductor, the conductor having a predetermined width and comprising a hole having a predetermined hole width through an entire thickness of the conductor; and a magnetic sensor for measuring at least one component of the magnetic field generated by the conductor. The magnetic sensor overlaps the aperture. Current sensing is based on the measured magnetic field. The sensor is positioned a predetermined distance above the top surface of the conductor. The width of the hole is at least 0.15 times the width of the conductor.

Description

Current sensing with positional stability

Technical Field

The present invention relates to the field of current sensing. More particularly, it relates to contactless sensing of current flowing through a conductor.

Background

Current sensing on bus bars is an important issue in electrical engineering. For example, in the automotive industry, energy generation and battery management systems require careful monitoring of the electrical power generated, distributed and stored by the vehicle. One method for current sensing involves the implementation of a contactless current sensor. These sensors typically operate by detecting a magnetic field generated by a current flowing through the bus bar. The sensing element generates a signal dependent on the magnetic field to which the sensing element is exposed. From this signal, it is possible to calculate the intensity of the current flowing through the bus bar.

Due to the nature of the magnetic field and the potential effects of ambient magnetic noise, the signal-to-noise ratio is an important parameter to be added in these sensors. This is achieved by positioning the sensing element very close to the bus bar in order to reduce the influence of ambient magnetic noise and also to increase the magnetic signal, since the magnetic force is greatly reduced by the distance. The bus bar may also be adapted by adding necking (pinning) near the sensing region, so that the magnetic field generated by the conductor increases locally around the necking. However, careful calibration is required for repeatability and reliability, which is difficult and time consuming.

Disclosure of Invention

It is an object of an embodiment of the invention to provide: a contactless sensing system for providing a stable reading of the current through a conductor, wherein the system has a high mechanical tolerance; and a method of setting up such a system, wherein time consuming positioning and calibration is not required. It is a further object to provide a component (part) kit comprising a conductor and a sensor.

In a first aspect, the present invention provides a sensing system for contactlessly sensing a current flowing through a conductor. The system comprises: a conductor for generating a magnetic field when a current flows through the conductor, the conductor having a predetermined width and comprising a hole having a predetermined hole width through an entire thickness of the conductor; and a magnetic sensor for measuring at least one component of the magnetic field generated by the conductor. The magnetic sensor overlaps the aperture. Current sensing is based on the measured magnetic field. The sensor is positioned a predetermined distance above the top surface of the conductor. The width of the hole is at least 0.15 times the width of the conductor. The sensor is centered with respect to the hole so that the central axis of the hole overlaps the sensor, e.g. intersects the center of the sensing area of the sensor.

An advantage of embodiments of the present invention is that the tolerance of the sensor positioning is improved. Further advantages are that static and dynamic mechanical tolerances are increased, thus reducing calibration requirements in the production line and reducing the effects of vibrations and lifetime mechanical drift.

In some embodiments of the invention, the sensor comprises at least one magnetic sensing element. In particular, the sensing element overlaps the hole of the conductor.

An advantage of embodiments of the present invention is that highly sensitive sensing elements may be used.

In some embodiments of the invention, the sensor includes a molded integrated circuit and leads, wherein the molded integrated circuit is disposed over the conductors separately. An advantage is that a modular system can be provided.

In some embodiments of the invention, the sensor is positioned between 1mm and 6mm from the conductor.

An advantage of embodiments of the present invention is that a compact design can be obtained while providing good mechanical stability.

In some embodiments of the invention, the sensor is adapted to measure a difference in field between two different positions.

An advantage of embodiments of the present invention is that the measurement of the field gradient is robust with respect to external magnetic fields.

In particular, the sensor may be adapted for measuring a difference in field between two positions in a perpendicular direction with respect to the conductor surface.

In a particular embodiment, a central axis may be defined in the bore, and the sensor further includes at least two sensing elements spaced apart in a plane parallel to the conductor surface, the central axis of the bore passing through a midpoint between the two sensing elements.

However, the invention is not limited to measuring differential fields. For example, the component of the field may be measured. For example, the X component of the field perpendicular to the direction of the current and the axis of the hole may be measured. This configuration advantageously simplifies the components, since only one sensing element may be required, and also the data processing of the signal may be simplified. Furthermore, the measurement of the X component exhibits high mechanical tolerances.

In some embodiments of the invention, the sensing system further comprises a magnetic shield at least partially surrounding the conductor portion comprising the aperture. In some embodiments, the magnetic shield has a U-shape.

An advantage of embodiments of the present invention is that mechanical tolerances are further improved.

In some embodiments of the invention, the sensor is adapted to provide a reading of the alternating current.

An advantage of embodiments of the present invention is that at least one component of the field is robust with respect to frequency dependent attenuation.

In some embodiments of the invention, the hole is centered with respect to the conductor cross-section.

In some embodiments of the invention, the conductor has a rectangular cross section and a thickness of 1mm to 5 mm.

In some embodiments, the conductor has a width between 3mm and 20 mm.

In a further aspect, the invention provides a method of measuring current through a conductor comprising providing a hole through the conductor, providing a magnetic sensor overlapping the hole at a predetermined distance from an opening of the hole, wherein providing the hole comprises providing the hole with a width of at least 0.15 times the width of the conductor.

An advantage of embodiments of the present invention is that a contactless sensor with high mechanical tolerances reduces or eliminates the need for accurate positioning and calibration during manufacturing. A further advantage is that mechanical tolerances during the lifetime of the device are also increased.

In some embodiments of the invention, providing the hole comprises stamping the conductor.

An advantage of embodiments of the present invention is that no complex and time consuming shaping or cutting methods are required to provide such holes on the bus bar. A further advantage is that this method is compatible with typical bus (bus) geometries, where the width of the bus is greater than the bus thickness (w > t), and has a suitable hole geometry, where the hole width is greater than the bus thickness (overall > t).

Particular and preferred aspects of the invention are set out in the appended independent and dependent claims. Features from dependent claims may be combined with those of the independent claims and with those of other dependent claims as appropriate and not merely as explicitly set out in the claims.

These and other aspects of the invention will be apparent from and elucidated with reference to one or more embodiments described hereinafter.

Drawings

Fig. 1 shows a bottom view of a conductor comprising holes, wherein the sensor overlaps the holes, according to an embodiment of the invention.

Fig. 2 shows a schematic diagram of a detection portion of a system according to an embodiment of the invention.

Fig. 3 is a graph of the field component (in mT) as a function of sensor-to-conductor distance for the case of no hole conductors (shielded and unshielded) and for the case of an embodiment of the invention (shielded and unshielded).

Fig. 4 shows a bottom view of a sensor adapted for measuring magnetic field gradients for use in an embodiment of the invention.

Fig. 5 shows differential field drift relative to sensor-to-aperture distance. For the cross section of the exemplary conductor shown in fig. 2, fig. 5 shows that there is a distance of the stable region where the signal due to positioning does not change by more than 2%.

Fig. 6A and 6B are graphs of a linear relationship between distance to a stable region and geometry of a conductor and its aperture according to an embodiment of the invention.

Fig. 7 shows a cross-sectional view of a detection portion of a shielded conductor including different sensors, according to an embodiment of the invention.

Fig. 8 shows a bottom view of a system including an AC power source according to an embodiment of the invention.

Fig. 9 is a graph of attenuation for AC at a frequency of 1.5kHz, for non-porous shielded and unshielded conductors, and for porous shielded or unshielded conductors, according to an embodiment of the invention.

Fig. 10 shows three graphs of the behavior of the field, attenuation and phase shift with the frequency of the alternating current for a non-porous shielded conductor.

Fig. 11 shows three graphs of the behavior of the field, attenuation and phase shift for a shielded conductor with holes as a function of frequency of alternating current, according to an embodiment of the invention.

The drawings are illustrative only and not limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

Any reference signs in the claims shall not be construed as limiting the scope.

The same reference numbers in different drawings identify the same or similar elements.

Detailed Description

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The dimensions and relative dimensions do not correspond to actual reductions in the practice of the invention.

Furthermore, the terms first, second, etc. in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence in time, space, in a rank, or in any other way. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Furthermore, the terms top, under and the like in the description and in the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noticed that the term 'comprising', used in the claims, should not be interpreted as being limitative to the means listed thereafter; it does not exclude other elements or steps. Thus, the term should be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the term "comprising" encompasses both the situation in which only the recited features are present and the situation in which these features and one or more other features are present. Therefore, the scope of the expression "an apparatus including the devices a and B" should not be interpreted as being limited to an apparatus constituted only by the components a and B. This means that for the present invention the only relevant components of the device are a and B.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner as would be apparent to one of ordinary skill in the art in view of this disclosure in one or more embodiments.

Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some features included in other embodiments but no other features included in other embodiments, combinations of features of different embodiments are intended to fall within the scope of the invention and form different embodiments as would be understood by one of skill in the art. For example, in the appended claims, any of the claimed embodiments may be used in any combination.

In the description provided herein, numerous specific details are set forth. It is understood, however, that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

In reference to "holes" in embodiments of the invention, reference is made to apertures through the entire thickness of the body, wherein the holes are surrounded by the material of the body except on two openings of the holes on opposite surfaces of the body. In an embodiment of the invention, the body is a conductor, typically a flat conductor such as a bus bar. The holes in the conductor are different from the necking or notching in the conductor. Topologically, a conductor with one hole is a class 1 (genus-1) surface.

In many instances, it is desirable to measure the amount of current through, for example, conductors on a circuit substrate (PCB) or conductors external to the board, such as bus bars or the like. The type of application generally defines the type of conductor; for example, bus bars are generally preferred for measuring currents estimated to exceed 30A. The types of applications include, but are not limited to, power generation, power storage and management (e.g., in the automotive industry), and/or power distribution in buildings, etc. The current generates a magnetic field that is detectable by one or more magnetic sensing elements. For example, depending on the type and number of sensing elements used, at least one component of the magnetic field may be measured. The sensing element generates a signal proportional to the detected magnetic field, which in turn is proportional to the current through the conductor. Thus, the current through the conductor may be obtained by measuring the electric field generated by the current through the conductor. Such current sensors are contactless current sensors in that they do not need to contact or otherwise mechanically interact with a conductor.

It is evident that the measurement of the current depends on the quality of the magnetic field measurement. The magnetic signal from the conductor should be high compared to noise (high signal-to-noise ratio), and the magnetic stray field should affect the magnetic signal as little as possible. It is not sufficient to place the sensor only very close to the conductor.

Existing solutions include necking of conductors. Since the sensor captures a small portion (the detection portion) of the magnetic field passing through the conductor, reducing the cross section of the conductor will locally increase the current, and thus the magnetic field generated by it, without significantly affecting the overall electrical signal passing through the conductor.

However, the positioning of the sensor must be very accurate and require expensive and time-consuming calibration. Furthermore, in some applications, the sensor may shift during the lifetime of the device due to, for example, vibrations or the like.

The present invention provides a sensing system in which the sensor placement requirements over the detection portion are relaxed. This means that the calibration requirements are also relaxed. Since the mechanical stability of the system is improved during the service life of the system, its advantages extend beyond the production phase. The measurement of the AC signal will suffer less attenuation.

The present invention provides a system wherein a so-called probing section separates a conductor into two separate components, wherein current flows in the same direction and with substantially the same strength through the two separate components. In other words, the detection portion of the conductor includes a hole. The sensor is placed over the aperture, overlapping the aperture. For example, the sensors are placed at the same distance from each component of the conductor.

Each component of the conductor acts as a smaller conductor around which a magnetic field is generated that interacts with magnetic fields generated around other components of the conductor. The magnetic field inside the well is very strong and therefore in order to obtain a good signal with a high SNR, measurements will be made inside the well. However, the present invention provides the opposite: the sensor is placed outside the hole at a predetermined distance, which depends on the characteristics of the conductor. For example, the spacing of the two components given by the width of the hole is adjusted such that there is a region above the hole at a predetermined distance from the conductor within which the measurement of the field has a very low sensitivity with respect to the location at which the measurement is being performed. When referring to a "stable region" in an embodiment of the invention, reference is made to a region where the signal varies by at most 4% (e.g. 3%, e.g. 2%) for the same current (thus, the variation results from sensor positioning).

While the necking of the prior art increases the SNR by reducing the cross section of the detection portion, a 1mm misalignment of the sensor above the expected position (e.g., for measuring the field gradient) can result in a deviation from the correct signal of up to 30%. To address this problem, accurate calibration is required and vibration or misalignment during the life of the prior art system can cause drift. The inventors have found that in embodiments of the invention, the size of the stable region is large enough to reduce calibration requirements, or even eliminate the need for calibration, despite the reduced magnetic signal due to the relatively large aperture width required. Since the stable region depends on the shape of the detection portion of the conductor, the influence of vibrations and/or displacements is reduced during the lifetime of the system.

In a first aspect, the invention relates to a sensing system for contactless current sensing. The system includes a conductor that, in operation, carries a current to be sensed. The system further comprises a magnetic sensor for sensing a magnetic field locally around the conductor, e.g. at least one component of the magnetic field, in the detection portion of the conductor. The magnetic sensor may provide a signal based on the sensed field. Since the signal is based on a magnetic field and the magnetic field is generated by a current through the detection portion of the conductor, the signal from the magnetic sensor can be used to provide a (magnetic, and thus contactless or contactless) measurement of the current through the conductor.

In the detection section, the conductor is divided into two parts, which produce substantially the same magnetic field around them, e.g. the same current through each part. These components are sufficiently separated to provide a magnetic field in which a large stable region exists. Each component of the conductor may be made of, for example, the same material, and it may be, for example, the same material as the rest of the conductor. For example, each component may be thinner than the rest of the conductor that is located outside the detection portion. In a particular embodiment, the conductors comprise through holes separating the conductors in the two parts of the detection portion. In this case, the width of the holes is adapted to provide the required sufficient spacing, taking into account the SNR and based on parameters of the conductor (e.g. the specific shape of the detection portion).

The characteristics of the sensor are such that one or more sensing elements can provide a signal based on the field within the stable region. The magnetic sensor is positioned a predetermined distance away from the aperture over the conductor such that the one or more magnetic sensing elements fit within a stabilizing region created over the region between the two conductor components (e.g., over the aperture in the conductor detection portion).

Fig. 1 shows a bottom view of an embodiment of the system 100 of the present invention, the system 100 comprising an elongated conductor 101, wherein the detection portion 103 comprises a hole 102, e.g. only one hole 102, wherein the center of the hole intersects the longitudinal center axis of the elongated conductor 101. The conductor 101 may be, for example, a bus bar. The current I flows in the longitudinal direction of the elongated conductor 101 as indicated by the arrow.

In some embodiments, the conductor 101 passing through the detection portion 103 has the same width as the rest of the conductor 101 (between the outer edges of the conductor 101). In some embodiments, the conductor 101 passing through the detector portion has straight edges because necking, notches, etc. are not required. In other words, there is no necking on the probe portion of the conductor. This improves the mechanical robustness of the conductor and simplifies manufacture as no necking needs to be provided.

The magnetic sensor 200 is disposed above the detection section. The magnetic sensor 200 overlaps the aperture 102, preferably centered on the axis of the aperture. Specifically, the sensor includes one or more sensing elements positioned proximate to the center of the aperture. For example, if there is one sensing element, its position may overlap the center of the hole 102, e.g., for multiple sensing elements (e.g., two), if there are multiple sensing elements, the midpoint between the sensing elements coincides with the center axis of the hole. The area or area of the sensor receiving the signal to be read (as projected from the top view) may be defined as the sensing area. When the sensor is centered about the central axis of the hole, it means that the sensor sensing area is centered about the axis of the hole 102. The sensing area of the sensor is defined by the sensing element. If one sensing element is present, the area of the sensing element itself (as projected from the top view) is centered on the axis of the hole. If there are multiple sensing elements, a pattern may be formed with the apex of the pattern at the center of each sensing element. The center of the sensing area surrounded by such a pattern is aligned with the axis of the hole. Thus, a single sensing element will be equidistant from each component of the conductor, with the aperture 102 having one component 104, 105 of the conductor at each side. For the plurality of sensing elements explicitly shown in fig. 2, the distance of each sensing element 201, 202 to the component 104, 105 of the conductor closest to the respective sensing element is approximately the same (thus, the sensing element 201 on the left is located at a given distance to the left side component 104 of the conductor and the sensing element 202 on the right is located at the same given distance to the right side component 105 of the conductor).

The magnetic sensor 200 may be an integrated circuit. The magnetic sensor may comprise at least one magnetic sensing element. Magnetic sensing may be based on magneto-resistive, hall sensing elements, or any other suitable sensing technique that may generate a readable signal based on (and proportional to) a magnetic field. In some embodiments, at least one hall element is used. This type of sensing provides an efficient, sensitive measurement with little power consumption.

The magnetic sensor may be, for example, a molded IC including leads or the like, as shown in fig. 2. Specifically, the sensor 200 of fig. 2 is a differential sensor comprising two sensing elements 201, 202 overlapping the aperture 102. A typical spacing between sensing elements may be between 1mm and 3 mm.

Such a magnetic sensor 200 may be provided on a substrate 210 comprising conductive traces or the like for outputting signals from the IC to a memory, display, controller, processor or the like. The substrate 210 may be, for example, a Printed Circuit Board (PCB). The substrate 210 and the sensor 200 may be separate and apart from the conductors, thus advantageously providing a modular system. The substrate 210 may also be arranged above and below, for example, a PCB may be mounted on the conductors. For example, conductors with holes of the correct size may be provided separately from the sensor. A simple guiding system can be provided which is adjusted to the hole to lock the positioning of the sensor. During assembly, the sensor 200 needs to overlap the hole 102, in particular the magnetic sensing elements 201, 202, at a predetermined distance from the hole 102, but the mechanical tolerance is too high to be positionable with an accuracy of e.g. a few millimeters, thereby improving the error tolerance and eliminating the need for complex calibration. Because of the ease of assembly, complex calibration is not required, the system can be provided to the end user or installer as a separate component in a conservative manner, and the system can be assembled in situ, for example, during the assembly of the structure to which the system belongs (e.g., a vehicle). However, the present invention is not limited thereto. In some embodiments, the conductors may be integrated or part of the same substrate provided with the sensor. For example, the conductor may be part of the substrate, so the conductor and the magnetic sensing element may be molded together.

Fig. 1 and 2 show that the Y-direction is the direction of the current, the Z-direction is the direction of the hole (or in other words, the direction perpendicular to the plane of the conductor surface (in the conductor section away from the detection section)), and the X-direction is perpendicular to the other two directions. In the case of the conductors of fig. 1 and 2, the X direction is the direction of the width Wh of the conductor, the Y direction is the direction of the current, and the Z direction is perpendicular to both in the thickness direction of the conductor. The remainder of this disclosure will follow the same orientation system.

The specific geometry of the detection portion of the conductor plays a role in the creation of a region where the mechanical tolerance is relaxed and the robustness to mechanical displacement is improved, in particular the distance Z0 between this region and the opening of the hole. This area determines the position where the sensor (more specifically the position of the sensing element) should be placed relative to the conductor.

In order to provide a sufficiently large stabilizing area over the hole to fit the sensing element, the separation of the two conductor parts (given by certain dimensions of the hole, in particular Wh) needs to be adapted and adjusted.

The length L of the hole (i.e. in the direction of the current flow) may be between 0.5Wh and 2Wh, or between 0.3Wh and 3 Wh. For example, for a square hole, the length of the hole may be equal to Wh. In some embodiments, L is at least 1mm, or at least 2mm, at least 3mm and/or 4mm, or 5mm or 6mm. The width Wh of the aperture is at least 0.15 times, such as at least 0.2 times, the width Wa of the conductor, and thus the width of the aperture is at least 15% of the width Wa of the conductor, or 20% or more, such as at least 30%, such as at least 35%, such as at least 40%, such as at least 45%, such as at least 50% of the width Wa of the conductor, these aperture dimensions resulting in relatively large aperture opening areas in some embodiments of the invention, which may theoretically accommodate the magnetic sensor 200. However, the sensor (and in particular the sensing element of the sensor) is located outside the conductor 101 at a predetermined distance from a plane defined by the surface of the conductor 101, as shown in fig. 2 below. For example, the sensing element is located in a plane parallel to the conductor surface (in other words parallel to the opening of the hole).

Fig. 2 shows a cross section II-II of the system as shown in fig. 1. The cross section of the detection portion of the conductor 101 as a bus bar is a rectangle having a predetermined width Wa and thickness t. The two parts 104, 105 are then separated by a distance equal to the hole width Wh. The aperture 102 may be arranged such that the magnetic fields generated by the conductor parts 104, 105 at two opposite sides of the aperture are substantially symmetrical mirror symmetry. For example, the hole 102 may be centered with respect to the cross-section X-Z of the conductor so that it intersects the longitudinal axis of the conductor. For example, the aperture may effectively divide the conductor 101 into two portions 104, 105, the two portions 104, 105 having equal cross-sectional areas as previously described, so that the current through the conductor is divided into two halves, each half flowing through one portion 104, 105 of the conductor. The magnetic field above the aperture includes an area of the magnetic sensor that is less affected by mechanical tolerances

This area is located outside the aperture 102 at a predetermined distance Z0. The distance between the one or more sensing elements and the plane of the conductor surface should be about Z0. In other words, the distance from the longitudinal axis at the center of the conductor 101 to the opening of the hole (t/2 in fig. 2) is smaller than the distance from the longitudinal axis at the center of the conductor 101 to the sensing element of the magnetic sensor 200 (or to the nearest sensing element) (t/2+z0 in fig. 2). Z0 is measured from the sensing element, e.g. from a plane containing the sensing element.

Furthermore, the projection of the one or more sensing elements over the hole is located at a distance of at least 0.1Wh from the conductor (or in other words from the inner edge of the hole).

The measurement of the sensor and magnetic field will be discussed below with respect to positioning over the aperture in the detection section. In some embodiments, the sensor may be adapted to provide a signal based on one or more components of the magnetic field (e.g., based on parameters derived from the one or more components). For example, in some embodiments, one or more of the sensing elements may include a magnetic concentrator, e.g., an Integrated Magnetic Concentrator (IMC), for redirecting the field or at least some components of the field to a sensing portion (e.g., to a hall plate).

In some embodiments of the invention, the sensor may be adapted to provide a signal based on only one component of the magnetic field (e.g. the X component Bx). In such an embodiment, only a single sensing element may be required in the sensor. This has a simple implementation and signal processing. In some embodiments, the single sensing element is centered with respect to the aperture. This means that the sensor should be positioned such that the axis of the hole passes through the sensing element. In some embodiments, this location exhibits a high degree of field symmetry. In particular, the measurement of the component Bx advantageously exhibits a high stability to mechanical tolerances, as follows. Such a sensor 220 is shown in the particular embodiment of fig. 7, and fig. 7 also shows an optional shield 111 as discussed below.

Fig. 3 is a graph showing the magnetic flux density (in mT) of the X component of the magnetic field versus the distance (z=z0+t/2) from the center of the conductor for four different configurations. The area between 0 and 1.5mm corresponds to the interior of the bus bar, i.e. between 0 and t/2. For both shielded enclosures 402, 404, a lower maximum field at (or near) the surface of the conductor is illustrated. The curve 402 without holes and with shields shows a steady decrease with distance at a similar rate as the curve 404 with holes with shields. On the other hand, for the case of a perforated conductor, the graphs 401, 403 show that the field increases from the surface, then a smooth maximum, having a plateau shape, then decreases until the field is similar to that in the case of a non-perforated, at a distance of about 8 mm. In the case of a shielded conductor with holes, the plateau is reached at about 4mm, while in the case of an unshielded conductor, the plateau is reached at about 3.5mm (relative to the center of the conductor).

Thus, if the sensor is placed around the platform, there is room for accurate positioning of the sensing element, thereby increasing mechanical tolerance, repeatability and life drift relative to the absence of holes. Less calibration is required than in the case of a non-porous conductor, where a half millimeter offset may result in a variation of a few mT for the same current. The stable region may be obtained from a platform, wherein the field varies by up to +/-4%, such as +/-3%, such as +/-2%, with positioning. The stabilizing region may extend up to 2mm, or 3mm, or even more, for example up to 4mm.

The discussion of fig. 3 relates to the measurement of one field component, but the invention is not limited thereto. For example, the sensor may be adapted to provide a signal derived from the field, e.g. a characteristic or parameter derived from the field component, instead of the field component itself. These types of measurements offer different advantages, such as less influence by external noise or stray magnetic fields, thus improving SNR.

In some embodiments of the invention, the sensor may be adapted to provide a signal based on the difference (or gradient) Δbz of the Z-component of the field at two different locations. In such an embodiment, two sensing elements may be used. For example, two sensing elements may be separated by a distance in the X-direction. For example, the sensor of fig. 2 comprises a first sensing element 201 and a second element 202, the first sensing element 201 being adapted to measure the Z-component of the magnetic field at a first location in a direction away from the conductor as indicated by the arrow, the second element 202 being adapted to measure the Z-component of the field at a second location. The Z component of the field has opposite signs at two locations, as indicated by the arrows.

Fig. 4 shows details of the sensor 200 of fig. 1 and 2. The sensor includes two sensing elements 201, 202, the two sensing elements 201, 202 being located at two different positions separated by a predetermined distance in the X-direction, however the invention is not limited to this configuration and the two sensing elements 201, 202 may be separated in different directions. For at least one component, a gradient of the field may be obtained as a difference of the field between the locations. If desired, each sensing element may include an IMC to properly redirect the relevant component of the field (e.g., bz component) to the sensing portion of the element from which the differential field is available as a difference in signal. As previously explained, the sensor (in particular the previously defined sensing region) is centered with respect to the aperture. In some embodiments, the midpoint between the sensing elements is centered with respect to the aperture. For example, in some embodiments, the sensing elements (e.g., hall sensing elements) are separated by a distance between 1mm and 3mm, e.g., 1.5mm or 2mm, or 2.5mm, e.g., 1.8mm. However, both may be installed in the stable region at the same time. By making the spacing less than 3mm, the sensing elements can be mounted in a single IC.

Fig. 5 shows differential field drift (in percent) with respect to distance from the conductor surface plane (or opening of the hole) for the cross-section of the exemplary conductor shown in fig. 2. However, since FIG. 5 shows the differential field as a function of the coordinates of the midpoint between the sensing elements, in this example, each sensing element of the differential pair is not within the stable region. Specific dimensions of the conductor in cross section include a thickness of 2mm, a hole width Wh of 2mm and a conductor width of 7mm (which means that the width of each component is 2.5mm assuming they are equal). The stabilizing zone is located at a distance Z0 of about 2.4mm (distance Z0 above the plane of the bus bar surface). Drift was reduced to a maximum of 2% for a change in dz of +/-0.5mm in this region.

This means that a sensor adapted to provide a differential field (e.g. a sensor with a pair of sensing elements as shown in fig. 4 and 2) should be placed at about 2.4mm from the plane facing the conductor surface of the sensor (being the top surface). The position may vary upwards or downwards between 1.9mm and 2.9mm and the drift will not vary by more than 2%. This means that the positioning does not require a time-consuming and very accurate procedure. This also means that mechanical strain (e.g., due to thermal expansion, vibration, etc.) during the lifetime of the device will not cause severe drift.

Other types of sensors also benefit from a stable region. For example, a sensor adapted to provide a signal based on one component (e.g. at least Bx) may also be placed in a stable region with high mechanical tolerance, at least in the Z-direction as shown in fig. 3.

The distance Z0 from the plane of the surface to the center of the stable region is measured, but the size of the stable region depends on the type of sensing. In other words, the distance range over which the signal is stable with respect to displacement should also be optimized to take into account the type of sensing, and which is affected by external factors such as shielding from stray magnetic fields. Typically, the distance Z0 may be between half the hole width Wh and twice the hole width Wh, or, for example, between 0.75 times the hole width Wh and 1.5 times the side hole width. In some embodiments, the distance Z0 between the one or more sensing elements of the sensor and the conductor 101 is between 1mm and 6 mm.

For many conductor configurations, many sensor types and good mechanical stability, a compact design can be obtained.

For example, for a sensor adapted to provide a differential field in the Z direction, or for a sensor adapted to provide a measurement of a field in the X direction, the range typically falls between 1mm and 4mm if the system does not have a special shield against stray magnetic fields or the like. For a system with a shielded version of a sensor adapted for measuring a field in the X-direction, see below with reference to fig. 7.

In some embodiments, the width of the aperture is greater than or equal to the thickness of the conductor (e.g., bus bar). This allows the holes to be provided by stamping.

The value of the distance Z0 to the stabilization zone may be related to the geometry of the bus bar having a width W, a thickness t, and a hole having a hole width Wh. It has been found that for the same material, the relationship between the geometry of the bus bar and the distance Z0 follows a linear relationship:

Z0-0.6W+0.2t＝a*Wh+b

where a and b are two constants, and where coefficients 0.6 and 0.2 apply to the Bz differential sensor. However, other values may be applied (e.g., different values will apply to Bx sensing). The spacing between the sensing elements is fixed and the remaining ones of the parameters of the conductor geometry are adapted as shown in fig. 6A and 6B.

This relationship may be applied to a sensing system, wherein the sensor is adapted for example to provide a gradient of Bz (and/or a difference Δbz of Bz between two locations). This is shown in fig. 6A and 6B as a function of the hole width Wh in the range between 2mm and 5mm. Each graph represents a different thickness and component width w value, where the component width w is the same for each opposing component of the conductor, and thus the width of the conductor can be calculated as wa=2w+wh. The thickness values varied between 1mm and 4mm, while the part widths varied between 2mm and 5mm, including 2.5mm, 3mm and 3.5mm.

The relatively large gap and distance Z0 between the conductor and the sensor (or between the center of the conductor and the sensor, minus half the thickness of the conductor) reduces the SNR. Nonetheless, the present invention improves gain stability relative to mechanical tolerances. It can be used to avoid sensitivity of the sensor to positioning and reduce calibration requirements on the production line (e.g., avoid over-current detection threshold recalibration) (thus improving static mechanical tolerance). It also reduces the effects of vibration and life mechanical drift (thus improving dynamic mechanical tolerance).

In some embodiments, magnetic shielding is included to reduce the effects of external fields in the region between the sensor and the conductor. In some embodiments, the shielding means comprises a ferromagnetic shield surrounding the conductor and the sensor, such as a U-shaped ferromagnetic shield as shown in fig. 7. For example, the sensors 200, 220 may be placed between the opening of the U-shaped shield 111 ("the top open portion of the U") and the conductor at a predetermined distance Z0 from the opening of the aperture 102 and a sufficient distance D from the opening of the shield 111 to make the shielding effective. The preferred minimum distance may be 3mm, for example 4mm or 5mm. For example, the distance D may be between 5mm and 10mm, such as 6mm, or 7mm or 8mm. The U-shape may have an overall height typically between 10mm and 20mm (e.g. 12.5mm or 15 mm). The sensor is typically located at about half of this height. Other shapes may be used, for example, the shield may wrap around the sensor. In some embodiments, the ferromagnetic shield 111 comprises mu-metal. The invention is not limited thereto and other types of shields may be used.

Fig. 7 shows a sensor 220 having a single sensing element. The sensor is adapted to measure one component of the field (e.g. the field flux), such as the X-component (as indicated by the arrow), at a single location. The sensing element may comprise means for redirecting field lines, for example a magnetic concentrator such as the IMC shown previously. The characteristics of the sensor and shield may provide a wider stability area (for a particular measurement of one component, e.g., a particular measurement of the field in the X component) than an unshielded system. In some embodiments, the distance Z0 to the conductor (as previously defined) may be up to 6mm. In some embodiments, Z0 may be selected to be half the entire width up to twice the width of the aperture (between 0.5Wh and 2 Wh).

In an embodiment of the invention, the conductors carry Alternating Current (AC) in the system of the invention. The inventors have found that at least one component of the field is robust to frequency dependent attenuation. Thus, in embodiments of the present invention, the SNR of the sensing system may advantageously remain unchanged with respect to frequency, or at least be less affected than other prior art schemes.

Fig. 8 shows a conductor 101 carrying alternating current and the sensor is adapted to provide a reading of the AC. The sensor 200 may be adapted to provide a gradient of the field in the Z-direction. The invention is not limited thereto and the sensor may be a sensor 220 adapted to detect a field in one component, e.g. a sensor 220 as shown in fig. 7. The current source may provide a frequency of, for example, at least 100Hz, such as above 1kHz, above 10kHz, or even above 100kHz. The conductors may be coupled to AC source 300, and AC source 300 may be any suitable source, and AC source 300 may be connected to (e.g., in contact with) conductors, such as bus bars. Conductor 101 may also be connected to load 301 such that the load receives alternating current through conductor 101.

In addition to the AC source, in some embodiments, the detection portion includes a shield. This reduces the effect of stray fields. It has also proven advantageous for AC applications (measurement of AC intensity) because attenuation and phase shift can be reduced. The advantages of the configuration of the invention together with the configuration of the prior art will be explained based on the following figures of fig. 9 for a conductor portion (non-porous case) as a busbar having a thickness of 3mm and a width of 12mm for the prior art and for a conductor portion having the same geometry and a hole of 3mm width at the centre of the conductor (thus providing two conductor parts having the same cross section on each side of the hole). The shielding effect in each case was investigated.

Fig. 9 is a graph showing the attenuation of the magnetic field (in percent) as a function of distance from the center of the conductor (z=z0+t/2) when the frequency of the AC is 1.5kHz for four different configurations. The area between 0 and 1.5mm corresponds to the interior of the bus bar, i.e. between 0 and t/2. Graph 1001 of a prior art system without holes and shields shows a slow increase of more than 10mm towards no attenuation (because attenuation is negative). The plot 1002 without holes and with shields shows attenuation at a similar rate as the plot 1003 with holes and without shields, however, the last case shows a more linear increase. Graph 1004 for the case of a perforated and shielded screen shows a rapid increase towards no attenuation around 4.5 mm. Repeatability with respect to mechanical tolerances is improved compared to the non-porous case. It is thus possible to obtain an overlapping region in which there is at the same time a region of very low stability and attenuation with respect to the precise positioning of the sensor. The figure also shows that the dependence of the damping at 1.5kHz on the mechanical displacement can be damped at the dashed line location, so that the damping varies less with the mechanical displacement than in the non-porous case. The derivative is smaller than in the non-porous case.

Fig. 10 and 11 show the frequency dependence of a shielded system with a sensor adapted to measure one magnetic field component (e.g. Bx), fig. 10 for the prior art configuration and fig. 11 for the present invention. In particular, fig. 10 shows a simulation of the frequency variation of several parameters of a shielded system without holes in the conductor. In the top graph, the magnetic field (in mT) is shown as a function of frequency (Hz) for 5 different positional displacements. The maximum difference is about 5mT due to the different positioning. The middle plot shows attenuation change in percent for five different locations. The difference increases with frequency. For the lowest variation, the attenuation drops to-6% with frequency at a displacement of-1 mm in the Z direction, while at a displacement of +1mm in the Z direction, the attenuation drops to almost-9% with frequency. The bottom graph shows the phase shift (in degrees) versus frequency for the same five different positions. As before, the greatest difference occurs between-1 mm and +1mm displacement in the Z direction, while displacement in the X direction has less correlation. The maximum offset occurs at high frequencies, near 4 degrees for positive 1mm displacement in the Z direction and near 3 degrees for negative 1mm displacement (at about 2 kHz).

Fig. 11 shows simulation results of a shielded system in which the conductor has holes, while other conditions (current frequency, displacement) are the same as fig. 10, according to an embodiment of the present invention. The field is almost the same regardless of displacement (top graph). The attenuation shown in the middle graph is an average value, increasing from 0 to-3% at 2kHz with frequency, but AC is very repeatable with respect to mechanical displacement. In the lowest graph, attenuation is slightly improved (about half degree in the best case of a non-porous conductor), but repeatability is also greatly improved, as attenuation is almost the same for all displacements.

In a further aspect, the invention provides a kit of parts comprising a conductor 101, the conductor 101 comprising a hole 102 according to the first aspect of the invention, and a sensor for contactlessly sensing a magnetic field generated by a conductor in a conductor portion 103, the conductor portion 103 being a detection portion comprising the hole.

The kit may include a substrate 210 in which the sensor 200 may be disposed or attached to the substrate 210. The substrate may be a PCB.

Since the shape, size and distance of the stabilization zone depend on the geometry of the detection part, it is possible to provide a pre-calibrated guiding and positioning system for positioning the sensor. In some embodiments of the invention, the kit of parts may comprise a guiding system, such as a separate system or a system integrated in the conductor or in the sensor or in the PCB, for allowing easy positioning of the sensor such that the sensing element is located in the stable region above the hole.

In some embodiments, the kit includes a connector to a source, such as an AC source.

In some embodiments, the kit may include a shielding system, such as a shielding plate, such as a shaped shielding plate (having, for example, a U-shape, or wrapping around a sensor, etc.), for example, the plate may be a metal plate, such as mu-metal.

The shielding system and the positioning system may be integrated with each other or attached to each other to obtain a good positioning of all elements relative to each other. The base plate and the shield may be adapted to mate with each other, e.g. the PCB may comprise attachment means (holes, slots, clips, etc.) to secure the shield in place.

In a further aspect, the invention provides a method of measuring current through a conductor by using the system of the invention. The method comprises the following steps: providing a conductor; forming holes in the conductor to obtain a conductor 101 having holes 102 as described in the embodiment of the first aspect of the present invention; and positioning a magnetic sensor comprising one or more magnetic sensing elements over the aperture. For example, the measured current may be AC.

In some embodiments of the invention, the method includes providing the hole by stamping. This is a simple and quick way of providing holes faster than for instance cutting or drilling. Typical bus bar geometries (where the width Wa and width w of each component around the aperture of the bus bar is greater than thickness t) can be easily punched to provide apertures having a width Wh greater than the conductor thickness t (thus, w > t, wh > t).

Positioning is performed such that the sensing area of the sensor is located within the stable region, or at least the center of the sensing area is within the stable region, which is formed at a predetermined distance Z0 from the plane of the conductor (or at a distance z0+t/2 from the center of the conductor, where t is the thickness of the conductor). In some embodiments, magnetic sensing 228711 is 1chcn

The element is placed in the stable region.

The method may be applied to measuring current in an electric motor, for example measuring phase current in a 3-phase system, for example. In this case, AC is typically generated by an inverter.

Claims (15)

1. A sensing system (100, 110) for contactless sensing of a current through a conductor, comprising a conductor (101) for generating a magnetic field when a current flows through the conductor, the conductor having a predetermined width (Wa) and comprising a hole (102), the hole (102) having a predetermined hole width (Wh) through the entire thickness (t) of the conductor, and a magnetic sensor (200) for measuring at least one component of the magnetic field generated by the conductor, wherein the current sensing is performed based on the measured magnetic field, the magnetic sensor overlapping the hole, wherein the sensor is located at a predetermined distance (Z0) above a plane of a top surface of the conductor, wherein an axis through the thickness of the hole is defined at a center of the hole, and the sensor is centered on the axis of the hole,

Wherein the width of the aperture is at least 0.15 times the width of the conductor.

2. The sensing system of the preceding claim, wherein the sensor (200) comprises at least one magnetic sensing element (201).

3. The sensing system of claim 1 or 2, wherein the sensor (200) comprises a molded integrated circuit and leads, wherein the molded integrated circuit is separately disposed over the conductor (101).

4. The sensing system of claim 1 or 2, wherein the sensor is positioned between 1mm and 6mm from the conductor.

5. The sensing system of claim 1, wherein the sensor is adapted to measure a difference in the field between two different locations.

6. The sensing system of claim 5, wherein the sensor is adapted to measure the difference in the field between two positions in a vertical direction relative to a surface of the conductor.

7. The sensing system of claim 4 or 5, wherein the sensor further comprises at least two sensing elements spaced apart in a plane parallel to the conductor, a central axis of the aperture passing through a midpoint between the two sensing elements.

8. The sensing system (110) of claim 1, further comprising a magnetic shield (111), the magnetic shield (111) at least partially surrounding the conductor portion (103) comprising the aperture (102).

9. The sensing system of the preceding claim, wherein the magnetic shield (111) has a U-shape.

10. A sensing system according to claim 1 or 2, wherein the sensor is adapted to provide a reading of alternating current.

11. The sensing system of claim 1 or 2, wherein the aperture (102) is centered with respect to the conductor cross-section.

12. The sensing system of claim 1, wherein the conductor (101) has a rectangular cross section and a thickness of 1mm to 5 mm.

13. The sensing system of the preceding claim, wherein the conductor (101) has a width of between 3mm and 20 mm.

14. A method of measuring current through a conductor, comprising: providing a hole through the conductor; providing a magnetic sensor overlapping the aperture at a predetermined distance from the aperture opening, wherein an axis through the thickness of the aperture is defined at the center of the aperture, and the sensor is centered on the axis of the aperture, wherein providing the aperture comprises providing the aperture with a width at least 0.15 times the width of the conductor.

15. The method of claim 14, wherein providing the hole comprises stamping the conductor.

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